A cement admixture is widely used as a water-reducing agent for cement compositions such as cement paste, mortar and concrete, and has become essential in constructing civil engineering and building structures and the like from cement compositions. Such concrete admixtures increase the fluidity of cement compositions to thereby reduce the water requirement of the cement compositions, and therefore are effective in improving the strength, durability and the like, of hardened (cured) products. Among such water reducing agents, polycarboxylic acid concrete admixtures comprising a polycarboxylic acid copolymer exhibit superior water-reducing performance to naphthalene and other conventional water reducing agents, thus have already led to good results in many cases as high performance AE (air-entraining) and high-range water-reducing admixture.
Such cement admixtures are required to be able not only to show water-reducing performance in such cement compositions but also to improve cement compositions in viscosity to thereby facilitate the works at the sites of handling them. Thus, the cement admixture used as a water-reducing agent are required at the sites of civil engineering and building structure construction and the like not only to be able to show water-reducing performance by decrease in a viscosity of cement compositions but also to provide a viscosity in such the level that the works will be facilitated at the sites of handling them. If a cement admixture can exhibit such performance characteristics, it will improve the working efficiency in civil engineering and building structure construction and the like.
Meanwhile, regarding a dispersant for an inorganic powder, Japanese Kokai Publication Hei-9-248438 (page 2) discloses the dispersant containing a water-soluble co-condensate or a water-soluble polymer in which a random polymerization chain (A) of an oxypropylene group and/or an oxybutylene group and an oxyethylene group is introduced. However, when it is used in cement compositions as an essential components, there was a room for contrivance in order to further improve the working efficiency in a field of the sites of civil engineering and building structure construction and the like, by improving the retaining ability of fluidity of concrete at a manufacturing filed or at the sites of handling them and, at the same time, by improving the condition of concrete so that the workability of concrete becomes excellent.
In addition, Japanese Patent Application 2003-128594 proposes a cement admixture which improves water-reducing property of cement compositions to make a strength and durability of its hardening product excellent, and can realize such a viscosity that work is easy in a field handling them, by introducing an alkylene oxide part having 3 or more carbon atoms into an intermediate part which is a particular part of a polyethylene glycol chain of a polycarboxylic acid copolymer having a polyethylene glycol chain. However, in such the cement admixture, since hydrophobicity of a cement admixture is too strong, an adsorbing force onto cement is weakened and, in order to enhance a cement dispersing ability, an amount of a cement admixture to be added is relatively large, and there remains a problem that economical disadvantage is caused.